Fabric, in particular for an airbag

ABSTRACT

A fabric is described, in particular for an airbag, consisting at least partially of hollow filament yarns (K, S) made of a polymer material, wherein the fabric has a cover factor DG, according to Professor Walz, that is equal to the cover factor when using solid filament yarns of the same diameter.

The present invention relates to a woven fabric, particularly for an airbag comprising at least in part hollow filament yarns of a polymer material.

Such woven fabrics are known for example, from EP 0 616 061 B1 of AKZO in which the contact or filter wovens disclosed therein are woven with differing thread densities and yarns differing in diameter. The first disadvantage of this is that the woven is still too heavy despite the use of hollow threads, there being no need here to emphasize the ever-increasing demands in automobile production for a reduction in weight.

The woven solid and hollow threads in the woven fabric disclosed therein have the same denier since the inventor based his assumptions on the required high air permeability and high strength woven necessitating solid and hollow threads equal in yarn strength and thus equal cross-sectionally in material mass. Due to the differences in diameter of solid threads and hollow threads the result of working both types of thread into a textile web is a woven fabric haphazard in thickness due to the density of solid threads than that of hollow threads being higher. Also unfavourable is that such woven fabrics are difficult to coat evenly. Employing hollow threads may also add to the thickness of the fabric, resulting in voluminous airbags with the drawback of higher package volume. The woven fabric as it reads from EP 0 616 061 B1 varies regionally in cover factor and thus also in its air permeability which (unlike as deduced in EP 0 616 061 B1) is evident from the cover factor as correctly calculated by the method in obtaining the WALZ density. Differences in the air permeability of a woven fabric are highly unfavourable in the case of an airbag, since it makes it impossible to reliably define the “useful life” of the airbag, in other words how long it remains deployed in actually meeting its requirement.

It is known to enhance the thermal capacity of wovens with hollow fibers or incorporating hollow threads. To make use of this effect EP 0 616 061 B1 employs hollow fiber and solid fiber yarns differing in denier which, however, results in the drawbacks as already cited.

On top of this, it reads from EP 0 616 061 B1 that exceeding a hollow surface area percentage of 40% results in a stiffening of the fibers and thus a deterioration in the folding ability of the airbag woven whilst establishing, for example, that yarns made fully or partly of hollow fibers have a denier ranging from 200 to 1100 dtex with the problem that any smaller dtex proves difficult to produce and any larger dtex cannot be made use of because of the folding ability becoming so poor.

It is important to note that in this case producing the hollow filaments is achieved by maintaining the yarn denier with an increase in the lumen (filament void), i.e. resulting in the polymer material in the hollow filament jacket equalling the polymer material of the solid filament. Added to this is the lumen increasing the thread diameter. This is why although the structures described in EP 0 616 061 B1 require fewer threads/cm the interweave (ondulation) of the thicker yarns and thus also the resistance to unravelling in the weave of warp and weft threads are diminished, however. Apart from this the hollow filaments become all the more less flexible the thicker the thread walls (ring surface area) with the disadvantage of there being a higher resistance to ondulation.

The present invention is based on the object of proposing a woven fabric for an airbag in which the drawbacks of prior art are avoided or at least greatly diminished.

This object is achieved in accordance with the invention by a woven fabric, especially for an airbag, comprising at least in part hollow filament yarns of a polymer material, characterized in that said woven fabric features a cover factor with a WALZ density equalling the cover factor when employing solid filament yarns the same in diameter. The woven fabric in accordance with the invention now makes it possible to advantage to specifically utilize a property of hollow filaments in which the thermal capacity or thermal resistance of the woven fabric is enhanced with no change in the high cover factor and high edge comb resistance for a weight less than that of known woven fabrics. To advantage in employing hollow fiber yarns and solid fiber yarns in accordance with the invention, stiffness, thickness and cover factor remain constant. The edge comb resistance (a measure of the seam strength) is even increased to advantage. The woven fabric in accordance with the invention is especially suitable for airbags for passenger restraint systems in automotive and aircraft applications.

Because the diameter of hollow fiber yarns and solid fiber yarns is the same the woven fabric in accordance with the invention is lighter than an equivalent woven fabric except for the hollow fibers, this reduction in weight corresponding to the lumen percentage. It is fortunate that the packing density of an airbag made of the woven fabric in accordance with the invention remains constant so that there is no need to alter the module dimensions when making use of the woven fabric in accordance with the invention. Yet another significant advantage is that the lower weight of the woven now makes it possible to improve the mass acceleration during the highly dynamic deployment phase of the airbag to advantage. In addition to this the hollow threads the same in diameter e.g. in combination with solid threads can now be processed to advantage into a uniform textile web.

The present invention is based on a woven structure wherein

-   -   the denier of the hollow filaments becomes less with increasing         lumen percentage,     -   yarn diameter, thread density and cover factor remain the same,     -   the walls of the ring surface areas of the hollow filaments         become thinner with increasing lumen percentage, and     -   the equation: reduction in lumen percentage=reduction in weight         holds.

Definition of lumen percentage: the lumen percentage is an indication in percentage of the lumen (void) of a hollow filament as compared to the total cross section of the hollow filament.

Whilst as known from prior art woven fabrics a (negative) increase in the stiffness of the hollow filaments occurs the higher the percentage of the hollow surface area, in the design basic to the woven fabric in accordance with the invention the higher the lumen the thinner the wall of the ring surface area becomes which fortunately does not result in an increase in the flexural rigidity of the hollow filaments.

Due to the thinner wall of the ring surface area weaving the threads the same in diameter is done the same as with solid filaments. With woven fabrics having a high cover factor the actually round hollow filaments form at the interweaves the corresponding reversal by oval kinking, advantageously enhancing the edge comb resistance (more frictional resistance).

For example, in accordance with the invention hollow filaments can be woven in a thread sequence (warp and/or weft) of solid to hollow filaments, e.g. 1 thread solid filament and 1 thread hollow filament.

In making use of the woven fabric in accordance with the invention it is now possible to also employ to advantage a hollow thread in stitched weft technology (see German patent DE 101 15 890 B2) in zones of a one-piece-woven (OPW) airbag particularly exposed to thermal stress. This is possible only with the woven fabric in accordance with the invention because since all threads are the same in diameter the disadvantage of any thick/thin effect resulting in an uneven OPW surface can now be avoided.

In one advantageous aspect of the invention the woven fabric is characterized in that said hollow filament yarns have a smaller denier than solid filament yarns the same in diameter and made with the same polymer resulting in the many advantages to be further discussed later on. For instance, rigidity, thickness and cover factor of the woven are constant. This simplifies the production of uniform woven fabrics (see above). The edge comb resistance (as a measure of seam strength) is higher than that of comparable woven fabrics made of solid filaments.

In another advantageous aspect of the invention the woven fabric is characterized in that it comprises solid filament yarns the same in diameter and made of the same polymer and that the hollow filament yarns are arranged at predefined locations of a repeat in the warp and/or weft and are interwoven in a weave structure higher than L1/1 and with a higher thread density than that of a L1/1 weave structure. This now makes it possible to advantage to arrange the hollow fiber yarns, for example, in thermally critical zones of a woven fabric or OPW specific to the technological and design engineering requirements.

In yet another advantageous aspect of the invention the woven fabric is characterized in that it comprises solid filament yarns the same in diameter and made of the same polymer and in that the hollow threads are arranged in stitched weft technology in zones of a OPW particularly exposed to thermal stress whilst being interwoven to a higher degree and with a higher thread density as compared to a L1/1 weave. In still a further advantageous aspect of the invention the woven fabric is characterized in that the percentage of the hollow surface area of the hollow filament yarns is in the region of 20% and more which proved to be particularly an advantage in tests.

In another advantageous aspect of the invention the woven fabric is characterized in that the cover factor has a WALZ density greater than 100% which proved to be of special advantage as regards the strength of the woven fabric in an airbag employed as a passenger safety item.

In yet another advantageous aspect of the invention the woven fabric is characterized in that the cover factor has a WALZ density greater than 105%.

In still a further advantageous aspect of the invention the woven fabric is characterized in that the weight of the woven fabric employing hollow filaments is lower in the scope of the lumen percentage as compared to solid filaments. This lower weight of the variant of the woven fabric as compared to known prior art variants now achieves an improved mass acceleration to particular advantage during the highly dynamic deployment phase of the airbag.

In yet another advantageous aspect of the invention the woven fabric is characterized in that said effective denier relevant to establishing the WALZ density cover factor is higher than the denier at the start by the shrinkage as triggered.

In a further advantageous aspect of the invention the woven fabric is characterized in that hollow threads are incorporated in stitched weft technology in zones particularly exposed to thermal stress in an OPW airbag.

In another advantageous aspect of the invention the woven fabric is characterized in that said polymer material is polyester and a) the yarn diameter (d), b) the thread diameter per cm, c) the WALZ density cover factor DG, d) the thickness of the woven fabric and e) the weight of the woven fabric corresponding to that of a fabric woven from polyamide 6.6 solid filaments.

The woven fabric in accordance with the invention can thus also be woven with polyester yarns incorporating hollow filaments wherein the higher specific weight of the polyester as compared to that of polyamide as regularly employed nowadays is compensated by a correspondingly selected lumen of the hollow fibers due to the roughly 21% reduction in weight achieved in accordance with the invention.

In yet another advantageous aspect of the invention the woven fabric is characterized in that its thread density is the same as when employing solid filaments the same in diameter and with the same woven structure.

In still a further advantageous aspect of the invention the woven fabric is characterized in that its woven thickness is the same as when employing solid filaments the same in diameter and with the same woven structure.

In another advantageous aspect of the invention the woven fabric is woven as a OPW incorporating single-ply and two-ply zones characterized in that it comprises substantially elongated tubular structures or tubes running in the warp or weft direction, said single-ply zones containing hollow filaments.

Both from the above description as well as as listed in Tables A and B the example embodiments mainly involve a woven fabric featuring high density and being uncoated. Further advantageous aspects of the invention claim how it is possible to employ hollow filaments of a polymer material the lumen percentage of which corresponds to the reduction in the yarn denier and thus the yarn diameter correspondingly with no change to that of the corresponding solid filament thread having a denier which is higher by the lumen percentage, for example, as a tubed woven fabric incorporating tubes running in the warp or weft direction. For this purpose, because of the high tensile stress, two-ply woven tubes are incorporated with solid filaments in the direction of the tensile stress. The single-ply zones contain hollow filaments to save weight. The thread system (as a rule the weft threads) running transversely to the tubes can incorporate either solid filaments or hollow filaments or in an alternating sequence depending on the function involved.

In yet another advantageous aspect of the invention the woven fabric is characterized in that the thread system running transversely to the tubes can incorporate either solid filaments or hollow filaments.

In yet a further advantageous aspect of the invention the woven fabric is characterized in that the thread system runs transversely to the tubes in an alternating thread sequence.

In still another advantageous aspect of the invention the woven fabric is characterized in that the tubes running in the warp and weft direction are configured as hollow filaments and the single-ply zones are formed of solid filaments especially in the direction of particular tensile stress. This woven fabric has the following advantages: where the tubes need to comply with the function of being particularly suitable to withstand thermal stress/insulation, the tubes are produced in the warp and weft direction as hollow filaments, the single-ply intermediate zone then advantageously consisting of solid filaments in the direction of particular tensile stress.

Wovens featuring hollow filaments in the sense of the invention comprise a uniform surface (no thick/thin effects) making them excellently suitable for coating by means of which a woven fabric of hollow filaments features a specific additional function in which the weight of the coating is compensated for by the reduction in the basic weight of the supporting woven (hollow filament woven). In addition to this, the hollow filament located oval where interweaved results in a larger surface area for bonding the coating mass.

The woven fabric in accordance with the invention consisting of solid or hollow filaments featuring the same density, thickness or especially edge comb resistance is suitable for an engineered agglomerated filament system without influencing the seam structure. The examples described in the following involve either substituting solid filaments by hollow filaments or an agglomeration in engineering the weave.

For clarification it is understood that a woven fabric in accordance with the invention also includes a one-piece woven (OPW) airbag. I.e. an airbag might be produced from a sheet woven in accordance with the invention incorporating hollow fibers the same in thickness, alternating in warp and/or weft thread with solid fibers or might be produced in OPW technology.

The denier of a yarn is defined as the weight in grams (dtex) of a thread 10,000 m long and thus the denier equates to the basic surface area—where hollow filaments are concerned only of the ring surface area encompassing the void—of the thread mass multiplied by the specific weight and length of 10,000 m.

The thread diameter d of hollow filaments is equated from the total basic surface area F_(ring) plus F_(lumen) as follows:

$F_{{tot}\mspace{14mu} {or}\mspace{14mu} {ring}} = \frac{{dtex}\mspace{14mu} \left( {mm}^{2} \right)}{{g/{cm}}\; 3 \times 10\text{,}000}$

From F_(ring) the total surface area F_(tot) is equated in mm² taking into account the lumen percentage. The thread diameter d is equated with respect to the cover factor as formulated by the WALZ density as follows;

$d = \frac{\left. \sqrt{}{Ftot} \right.\mspace{14mu} ({mm})}{0.885}$

This terminology of the various terms involved presently serves to explain that hollow fiber yarns are hollow threads or synthesized filament yarns incorporating filaments having an internal void whose percentage of the hollow surface area is referenced to the total cross-sectional surface area of the filaments.

The German definition of cover factor (DG)as formulated by the WALZ density reads from “Die Gewebedichte I” and “Die Gewebedichte II” on pages 330 to 366 of the publication “Textilpraxis” dating back to 1947 published by the Robert Kohlhammer-Verlag in Stuttgart, Germany. Equating the cover factor DG is based on determining the yarn count, settings and knowing the density of the fiber material employed. The cover factor DG % as formulated by the WALZ density is

cover factor: DG %=(dk+ds)² . fk . fs

where: dk/ds=substance diameter of warp or weft yarn in mm; fk/fs=warp or weft thread count per cm;

The substance diameter of solid filament yarns equates as follows:

${dks} = \frac{\left. \sqrt{}{dtex}_{ks} \right.}{{88.5 \cdot \left. \sqrt{}{density} \right.}\mspace{14mu} {g/{cm}}\; 3\mspace{14mu} ({mm})}$

(Note that the above formula applies only to plain weaves (cover factor I), where other weaves higher than plain, i.e. L1/1 the resulting cover factors are to be multiplied by certain factors, e.g. twill 2:1=0.7, twill 2:2=0.56, twill 3:1=0.56, twill 4:4=0.38, satin 1:4=0.49, panama 2:2=0.56, in thus obtaining cover factor II).

Interpretation of equating cover factor (DG) as formulated by the WALZ density:

1. Effective Denier:

The effective denier equates from the circular surface area for solid threads and from the ring surface area for hollow threads.

2. Thread Diameter

The thread diameter (d) is relevant for calculating the cover factor and in the case of hollow filaments it equates from the total cross-sectional surface area (ring+hollow surface area).

3. How Thread Size, Density and Interweave Interrelate:

The surface area resulting for an interweave (in L1/1) equates from (dk+ds)² in mm². The quotient of 100 mm²: (dk+ds)² corresponds to the maximum number of interlacings per cm²=100%. The product of f_(k)×f_(s) corresponds to the number of interweaves attained per cm².

The following comments are illustrated by FIGS. 1 to 4 in which:

FIG. 1 is a diagrammatic illustration of a section of a weave design.

FIG. 2 is a diagrammatic illustration of an example of homogenous tile of polymer.

FIG. 3 is a diagrammatic illustration of an example of a “sandwich” tile.

FIG. 4 is a diagrammatic illustration of a warp and weft interweave of hollow filaments.

FIG. 5 is a diagrammatic illustration of an example of a tubed woven incorporating warp or weft tubes in a first variant.

FIG. 6 is a diagrammatic illustration of a further example of a tubed woven incorporating warp or weft tubes in a second variant.

Referring now to FIG. 1 there is illustrated diagrammatically a section of a L 1/1 weave design together with the corresponding warp and weft section.

Equating cover factor (DG) as formulated by the WALZ density is thus given by:

$\frac{100 \times {fk} \times {fs}}{\frac{100}{\left( {{dk} + {ds}} \right)^{2}}} = {{DG}\mspace{14mu} \%}$ (dk + ds)² × fk × fs = DG  %

The diameter (d) used as that of the thread is the geometric correct value in (mm), i.e. the substance diameter for solid filaments and the total diameter of ring and hollow surface area (F_(tot)) for hollow filaments.

EP 0 616 061 B1 teaches that just a 20% fraction of the hollow surface area increases the thermal resistance by approx. 175%. This conclusion is based on the following computation model: The assumed surface area of 1 m² with a weight of 210 g/m² is divided by the specific weight in g/m3. The result (FIG. 2) is the thickness dv of a homogenous polymer tile of 1 m², in the example cited, of 0.18 mm at PA 6.6.

Referring now to FIG. 2 there is illustrated an example of a homogenous polymer tile of 1 m².

The wall thickness as thus established is divided by the coefficient of thermal conductivity (□) resulting in the thermal resistance Rw (K/W) of the full surface area. The thermal resistance Rw of the hollow surface areas is computed on the same principle, e.g. for a lumen of 20% with two different media.

Referring now to FIG. 3 there is illustrated an example of a “sandwich tile” of 1 m² wherein the “outer walls” A encompassing the lumen L with a “thickness” of 0.036 mm have a thickness dh of 0.09 mm.

Summing the thermal resistances Rw of the wall and of the hollow surface area results in a thermal resistance approx. 175% higher than that of the solid surface area. Comparing the thermal resistance of a solid filament to that of a hollow filament with a lumen of 20%—as computed with the same parameters—results in a relative increase of Rw of >300% in the body of the yarn. In both models the thermal transition is assumed perpendicular or radial to the wall surface area. The model as it reads from EP 0 616 061 B1 is based on a closed polymer tile, not taking into account the structural features of a textile surface area (weave, ondulation), however.

By contrast, the model as it reads from the present invention is based on the geometrically correct structure of the yarn body but covers only the thermal transition in the radial direction. Taking into account the structure of the woven fabric (yarn body interweave, type of weave, cover factor %) the direction of the thermal stress differs with respect to the yarn body, i.e. radial to axial. In addition to this it needs to be remembered that when the thermal stress acts radially the thermal resistance in the ring surface area is less than in the lumen and thus the direction in which the thermal stress is active is non-linear.

Referring now to FIG. 4 there is illustrated diagrammatically a section of a plain weave (L 1/1) showing how the hollow filaments K and S are interwoven in the warp and weft direction. With thermal stress acting perpendicular to the textile surface area in the direction of the arrow V the thermal transition in the run of the thread correspondingly differs.

This results in the following advantage: when both solid filaments as well as hollow filaments are worked into a textile surface—or in OPWs—then in surface areas subjected to thermal stress the hollow filaments preferably also need to be woven in a more engineered structure, e.g. basket weave where the cover factor is higher (cover factor II).

Referring now to FIG. 5 there is illustrated a diagrammatic illustration of an example of a tubed woven incorporating tubes oriented in warp or weft direction in a first variant in which the reference numeral 2 identifies tubes incorporating solid filaments in the tensile stress direction shown, in this case as an example, in an “inflated” honeycomb structure. The reference numeral 4 identifies single-ply intermediate portions incorporating solid filaments in the tensile stress direction between the tubes 2 whilst reference numeral 6 identifies the corresponding system of solid or hollow filaments as transverse threads.

Referring now to FIG. 6 there is illustrated a diagrammatic illustration of a further example of a tubed woven incorporating warp or weft tubes in a second variant. In this variant the reference numeral 12 identifies tubes incorporating hollow filaments in the warp and weft direction shown, here as an example, in an “inflated” honeycomb structure. The reference numeral 14 identifies single-ply intermediate portions incorporating solid filaments in the tensile stress direction between the tubes 12 whilst reference numeral 16 identifies the corresponding system of hollow filaments as transverse threads.

To show how the invention can be engineered example variants thereof are summarized in the following.

Here the Example Variants I and II

TABLE A Comparison of a standard article to example variants I and II of the woven fabric in accordance with the invention Ex. I with predefined denier in same Example II with predefined cover factor Standard - Article cover factor with hollow filaments and D′ with hollow filaments starting denier - effective - dtex 474/72 380/72 390/72 nominal shrinkage - % 8.2 5.4 5.4 lumen - % — 20 20 F tot - mm² 0.04158 0.04167 0.042868 F ring- mm² — 0.03333 0.034294 = 80% F lumen - mm² — 0.00834 0.008574 = 20% D′ - mm 0.2304 0.23066 0.23395 warp count/dm 224.8 220 224.8 weft count/dm 209.2 220 209.2 basecloth weight - g/m² 239 189 193 crimp - % (K/S) 11/7 11/6 11/7 thread length/m² - m 2495 + 2238 = 4733 m 2442 + 2332 = 4774 m 4733 m effective denier dtex 505 396 407 F tot.- mm² 0.044295 0.04306 0.044295 F ring- mm² — 0.03472 0.035721 F lumen - mm² — 0.00834 0.008574 D′ - mm 0.2378 0.23447 0.2378 triggered shrinkage - % 6.14 4 4 cover factor DG - % 106.4 106.4 106.4 fabric thickness - mm 0.36 0.35 0.36 max. tensile stress - warp N/5 cm 3322 2603 2737 max. tensile stress - weft N/5 cm 3305 2786 2726 21% reduction in weight 19% reduction in weight

The above Table A compares a standard article (all-solid fiber) to example variants I and II (all-hollow fiber) of the woven fabric in accordance with the invention illustrating how substituting solid filaments by hollow filaments of the same polymer in a textile surface area of consistent cover factor achieves a reduction in the denier and in the weight of woven by the lumen percentage for the same thread diameter (d).

The intention is to substitute the high cover factor of the standard article (prior art) engineered in polyamide 6.6 (PA 6.6) solid filaments by a surface area engineered at least partly in PA 6.6 hollow filaments for the same cover factor.

The cover factor of the woven fabric is needed because of the LD in conjunction with with an uncoated application and high seam strength (edge comb resistance). As regards strength and weight the woven fabric as specified in the standard article is “over-engineered”.

Example Variant I

Example variant I is based on an existing yarn of PA 6.6 in a denier of 380/72 dtex with a lumen of 20%. Taking into account the specific shrinkage values—the ratio of the resulting shrinkage to the nominal shrinkage (hot air shrinkage of the yarn) being defined and depending on how it is finished—the corresponding number of threads of the finished fabric (22×22 Fd/cm) is established from the predefined cover factor of 106.4% as formulated by the WALZ density on the basis of the thread diameter in the finished fabric (after shrinkage).

The square meter weight as computed from thread densities, crimp and effective denier (after shrinkage) is lower by the percentage of the lumen (lumen %) and the maximum tensile forces in N/5 cm are correspondingly reduced.

Thanks to its cover factor the woven fabric has the necessary seam strength (edge comb resistance).

Example Variant II

In example variant II a woven fabric of PA 6.6 hollow filaments was produced having exactly the same parameters (cover factor %, thread diameter, thread density) as the “standard article”. Starting with the necessary effective denier as needed and taking into account the shrinkage value (triggered shrinkage) the nominally denier is obtained retrogradedly.

The reduction in the square meter weight corresponding to the lumen percentage and the maximum tensile forces in the warp and weft direction are reduced by the same percentage as practically the same absolute values because of the difference in the thread densities in the warp and weft direction. As regards a biaxial tensile stress of the woven fabric these same values are an advantage. The example variant II now makes it possible to substitute the so-called standard article woven fabric with improved technical conditions for its use (no longer “over engineered”, lighter) by a hollow filament woven fabric.

Example Variant III

Yet another example variant (III) will now be detailled with respect to Table B in reenacting the known standard article of PA 6.6 employing polyester hollow filaments having the same parameters as the finished woven. The approach is the same as that of example variant II in also proving that polyester can be put to use in airbag woven fabrics because of it being better cost-effective.

The intention is to produce the woven fabric (standard article) in a dense structure of PA 6.6, dtex 470, 22×21 with cover factor=106.4% in L 1/1 with the same density and same thickness (diameter) of the thread in making use of a corresponding PES hollow filament thread.

Substituting solid filaments by hollow filaments of another polymer material in a textile surface area having the same constant density results in the same denier and same woven weight—see Table B—for the same thread diameter (d) and a lumen % corresponding to the percentage of the difference in the specific weight of both polymers.

TABLE B PA-woven PES-woven standard- hollow- Term (dimension) article filament starting denier 474/72 477 effective in dtex lumen - % — 20 F ring [mm²] — 0.034582 F lumen [mm²] — 0.008645 F tot [mm²] 0.04158 0.043227 D [mm] 0.2304 0.2349 warp thread [/dm] 224.8 224.8 weft thread [/dm] 209.2 209.2 crimp -% [warp/weft] 11/7 2.9/4.8 fabric weight [g/m²] 239 222 thread length in [m/m²] 4.733 4.505,6 effective denier [dtex] 505 492 F ring [mm²] — 0.03565 F lumen [mm²] — 0.008645 F tot [mm²] 0.044295 0.044295 D′ [mm] 0.2378 0.2378 triggered shrinkage [%] 6.14 3 (0.97) cover factor DG - % 106.4 106.4

Using PES hollow filament with 20% lumen (void in the fiber) makes it possible to produce a woven fabric having the same cover factor, and this despite the higher special weight (+21%) in the same weight class.

Taking into account the differences in the yarn and shrinkage values and crimp conditions the reduction in weight equates to the lumen %.

Mixing hollow filaments the same in diameter in the textile surface areas of solid filaments results in the same cover factor and reduction in weight for the same weave (e.g. plain L 1/1). In zones particularly exposed to thermal stress the thread diameter for hollow filaments can be correspondingly increased by a higher weave structure for the same cover factor (DG II).

EXAMPLES

-   -   a) Sheet woven alternating 1 solid filament thread with 1 hollow         filament thread in the warp and weft direction, results in a         woven which is lighter with the same remaining structure.     -   b) Sheet woven incorporating hollow filaments in predefined         locations in the warp and/or weft direction in a higher weave         structure, results in enhanced resistance to thermal stress.     -   c) OPW employing hollow filaments in stitched weft technology,         also possible in a higher weave structure, results in enhanced         resistance to thermal stress. 

1. A woven fabric, especially for an airbag, comprising, at least in part, hollow filament yarns of a polymer material, wherein said woven fabric features a cover factor with a WALZ density equalling the cover factor when employing solid filament yarns the same in diameter.
 2. The woven fabric as set forth in claim 1, wherein said hollow filament yarns have a smaller denier than solid filament yarns the same in diameter and made with the same polymer.
 3. The woven fabric as set forth in claim 1, wherein the weight of said woven fabric employing hollow filaments is lower in the scope of the lumen percentage as compared to solid filaments.
 4. The woven fabric as set forth in claim 1, wherein said weave is structured as L1/1 or in a higher weave.
 5. The woven fabric as set forth in claim 4, further comprising solid filament yarns the same in diameter and made of the same polymer, wherein the hollow filament yarns are arranged at predefined locations of a repeat in the warp and/or weft and are interwoven in a weave structure higher than L1/1 and with a higher thread density than that of a L1/1 weave structure.
 6. The woven fabric as set forth in claim 4, further comprising solid filament yarns the same in diameter and made of the same polymer and that, wherein the hollow threads are incorporated in stitched weft technology in zones particularly exposed to thermal stress in an OPW airbag and are interwoven in a weave structure higher than L1/1 and with a higher thread density than that of a L1/1 weave structure.
 7. The woven fabric as set forth in claim 1, wherein said percentage of the hollow surface area or lumen percentage of the hollow filament yarns is in the region of 20% or higher.
 8. The woven fabric as set forth in claim 1, wherein said cover factor has a WALZ density greater than 100%.
 9. The woven fabric as set forth in claim 8, wherein said cover factor has a WALZ density greater than 105%.
 10. The woven fabric as set forth in claim 1, wherein said hollow filament yarns and solid filament yarns are polyester yarns.
 11. The woven fabric as set forth in claim 1, wherein said polymer material is polyester and wherein: a) the yarn diameter, b) the number of threads per cm, c) the WALZ density cover factor DG, d) the thickness of the woven fabric, and e) the weight of the woven fabric correspond to that of a fabric woven from polyamide 6.6 solid filaments.
 12. The woven fabric as set forth in claim 1, wherein said woven fabric features a uniform edge comb resistance.
 13. The woven fabric as set forth in claim 1, wherein a thread density (number of threads per cm) of the woven fabric is the same or higher as when employing solid filaments with the same diameter and with the same woven structure.
 14. The woven fabric as set forth in claim 1, wherein a woven thickness is the same or higher as when employing solid filaments with the same diameter and with the same woven structure.
 15. The woven fabric as set forth in claim 1, wherein the fabric is woven as an OPW incorporating single-ply and two-ply zones, wherein the fabric further comprises substantially elongated tubular structures or tubes running in the warp or weft direction, said single-ply zones containing hollow filaments.
 16. The woven fabric as set forth in claim 15, wherein said thread system running transversely to the tubes incorporates either solid filaments or hollow filaments.
 17. The woven fabric as set forth in claim 15, wherein said thread system running transversely to the tubes is configured in an alternating thread sequence.
 18. The woven fabric as set forth in claim 15, wherein said elongated tubular structures or tubes running in the warp and weft direction are configured as hollow filaments and the single-ply zones are formed of solid filaments especially in the direction of particular tensile stress. 